Liquid crystal display and a fabricating method thereof

ABSTRACT

The present invention relates to a liquid crystal display and a fabricating method thereof which prevent light leakage occurs near data lines in accordance with the rubbing direction of an alignment film. The present invention includes a thin film transistor plate having a gate line, a data line, a gate electrode, a thin film transistor, a passivation layer, and a pixel electrode, a color filter plate including a black matrix, a color filter and a common electrode on a second transparent substrate, and liquid crystals injected and sealed between the thin film transistor plate and the color filter plate, wherein the black matrix of the color filter plate is overlapped asymmetrically with the data line of the thin film transistor plate.

This application claims the benefit of Korean Patent Application Nos.1999-9018, 1999-9020, and 1999-9021, each filed on Mar. 17, 1999, andeach of which is hereby incorporated by reference for all purposes as iffully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display, and a methodof fabricating a liquid crystal display, which prevents light leakagefrom occurring near data lines in accordance with the rubbing directionof an alignment film.

2. Discussion of Related Art

A TFT-LCD (thin film transistor-liquid crystal display) is comprised ofa TFT array plate in which a plurality of TFT's and pixel electrodes arearranged, a color filter plate consisting of color filters and commonelectrodes, and liquid crystal filling up a space between the TFT arrayand color filter plates. Both plates are equipped with alignment filmsas well as attached polarizing plates which polarize visible rays.

A TFT-LCD having the above-mentioned structure has an advantage merit inpower consumption, compared to a cathode ray tube (CRT). Particularly,power consumption is the most important factor in a portable TFT-LCD.

Efficiency of a back light is reduced greatly during passing through apolarizing plate and color filters. For instance, only 38% of lightenergy penetrates through a commercial polarized plate, and 40% of lightenergy permeability of penetrates through color filters, and thecontrast and color reproductivity are reduced if light energy thepolarizing plate and color filters are increased. Instead, it is moreefficient to increase the opening ratios which is the ratio of areawhich permits the transmission of light in a unit cell.

FIG. 1 shows a layout of a unit pixel of a conventional TFT-LCD.

FIG. 2 is a cross-sectional view of an LCD having a TFT with an inversestaggered structure according to a related art, which is bisectedthrough the line I–I′ in FIG. 1.

FIG. 3 shows a cross-sectional view bisected through the line II–II′ inFIG. 1.

FIGS. 4A to 4C show cross-sectional views, which are bisected throughthe line II–II′ in FIG. 1, illustrating fabrication of an LCD accordingto a related art.

FIG. 5A shows a graph of equipotential potential lines between a TFTarray plate and a color filter plate in an LCD according to a relatedart, wherein a predetermined voltage is applied to the plates. FIG. 5Aalso shows potential difference and the generation of light-leakageregion B on data lines when light is cut off by liquid crystals betweenboth plates. FIG. 5B shows a cross-sectional view of an LCD where alight leakage region is generated, which points out a problem of therelated art.

Referring to FIG. 1 to FIG. 3, gate lines 10 are formed in a horizontaldirection on a transparent substrate 1, which is a TFT array plate onwhich TFT's and pixel electrodes are arranged. Data lines 20, crossingthe gate lines 10, are arranged in a perpendicular direction to the gatelines 10.

A gate electrode 14, extending from the gate line 10, is formedprotruding in the same direction as the data line 20.

An active layer 12, beneath which a gate insulating layer 22 lies, isformed on the gate electrode 14. A channel region is defined in theportion of the active layer 12 corresponding to the gate electrode 14.At either side of the channel region in the active layer 12, a sourceregion and a drain region are each defined.

A source electrode 16, connected to the source region of the activelayer, and a drain electrode 18, connected to the drain region of theactive layer, are formed in the same direction as the gate line 10 isaligned. The source electrode 16 and drain electrode 18 each protrudefrom the data line 20.

A passivation layer 24 covers the above structure. A contact holeexposing the drain electrode 18 is formed in the passivation layer 24.And, a pixel electrode 30 which is connected to the drain electrode 18and covers the contact hole is formed on the passivation layer 24.

The pixel electrode 30, beneath which the passivation layer 24 lies onthe data line 20, may have a structure such that the pixel electrode 30partially overlaps the data line 20 and generally the width of theoverlapped area, which is designated by the reference sign “A”, is under1.5 μm, in order to increase the opening ratio. The reference numeric 32indicates an opening of a black matrix (hereinafter abbreviated BM) 29of a color filter plate m which is shown in FIGS. 5A–B. Light rays areactually transmitted through the opening.

A process of fabricating an LCD having the above-described structureaccording to a related art is explained in the following description.

Referring to FIG. 1, FIG. 2 and FIG. 4A, after a metal layer has beenformed by sputtering Al, Mo or the like on a transparent substrate 1such as glass, in which gate and data lines are defined, gate lines 10are formed by patterning the metal layer. In this case, a gate electrode14 is also patterned which protrudes from the gate line 10 as soon asthe gate line 10 is patterned.

After a gate insulating layer 22 is formed to cover the gate electrode14, an intrinsic amorphous silicon layer and a silicon layer to which animpurity such as P is added to work as an ohmic contact layer aredeposited successively, and an active layer is formed by patterning theamorphous silicon layer and the impurity-contained silicon layer.

After a metal layer is formed on the above structure, data lines 20 arepatterned by etching the metal layer. When the data lines 20 arepatterned, source and drain electrodes 16 and 18 connected to the sourceand drain regions respectively are also patterned. The source and drainelectrodes 16 and 18 are arranged to overlap the gate line 10.

Although not shown in the drawing, the impurity-containing silicon layeris etched using of the source and drain electrode patterns as a mask todivide the ohmic contact layer inserted between the active layer and thesource/drain electrodes 16 and 18, into the portions for the source anddrain electrodes.

Referring to FIG. 2 and FIG. 4B, a passivation layer 24 is formed on theabove structure by depositing by CVD an insulating layer of siliconnitride or the like which has a low dielectric constant.

Referring to FIG. 2 and FIG. 4C, a contact hole exposing the drainelectrode 18 is formed in the passivation layer 24.

After ITO (Indium Tin Oxide) has been deposited on the passivation layer24, a pixel electrode 30 is formed by patterning the ITO to be connectedto the drain electrode 18. The pixel electrode 30, as mentioned in theabove explanation, has a structure overlapping with the data line 20.The width of the overlapped area A is less than about 1.5 μm.

Thus, a TFT array plate, on which TFT's and pixel electrodes arearranged according to a related art, is completed.

Referring to FIG. 5B, after liquid crystals 28 have been injectedbetween the TFT array plate

and the color filter plate m in which color filters and black matrix 29are fabricated, an LCD according to the related art is completed bycarrying out a sealing process. An alignment film (not shown in thedrawing) is formed on the color filter plate m and the TFT array plate

Liquid crystals between the color filter and TFT array plates arealigned uniformly by carrying out a process of rubbing the alignmentfilm with cloth.

It has been known that the LCD of the related art which has theabove-mentioned structure normally has no problem of light leakage, asthe data line and the pixel electrode overlap each other partially.Unfortunately, however, when voltage is applied between the color filterand TFT array plates m and

the light leakage problem does exist if that the overlap area betweenthe data line and the pixel electrode is under 1.5 μm, as explainedherein with reference to FIG. 5A and FIG. 5B.

FIGS. 5A and 5B show a pattern of cutting off light due to the liquidcrystal function when voltage is applied between the color filter andTFT array plates m and

which operate in a normally white mode, wherein the data line 20 isoverlapped by the pixel electrode 30 to a width of 1.5 μm in the TFTarray plate of the related art. Curves between both plates m and

are equipotential lines. Liquid crystals react with the equivalentpotential lines perpendicularly for the most part while the curves areslanted on the data line 20, due to the potential difference. FIG. 5Aalso shows the graph “P” indicating the permeability of light in thedevice.

Referring to FIG. 5A, when voltage is applied between both plates m and

the equipotential lines are deeply distorted, as the data line voltageinfluences the voltage applied to the liquid crystals. This influencedistorts the working orientation of the liquid crystals to be slanted,and also generates a region in which the light permeability is abruptlyincreased. This region lies on the pixel electrode and extends 1 μm to 2μm away from the area which is overlapped with the data line 20. Inother words, the region includes the area overlapped with the data line20, and the area designated by the reference indicator B in FIGS. 5A–B.

But, all of the above-mentioned light-transmitting region, which is thepart with the permeability peak in the graph “P” in FIG. 5A, does notinfluence the image quality. Namely, the overlap region (1.5 μm), atwhich the data line and the pixel electrode overlap each other, does notinfluence the image quality directly, as the area is overlapped so asnot to transmit the light. The other region B, in which the data line isnot overlapped by the pixel electrode, actually transmits the light tohave an effect on the image quality.

The above light leakage region B, which has no relation with thepolarity of the voltage applied to the pixel electrode adjacent to thedata line, may be generated at the right or left in accordance with therubbing direction of the alignment film.

Unfortunately, the product quality is reduced due to the generation ofthe light leakage region which is produced by the transmission of lightthrough the area B separated from the overlap area of 1.5 μm, betweenthe data line and the pixel electrode, where the liquid crystals take ona slanted orientation because of the potential difference.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a liquid crystaldisplay, and a fabricating method thereof, that substantially obviateone or more of the problems due to limitations and disadvantages of therelated art.

An object of the present invention is to provide a liquid crystaldisplay which prevents the transmission of light generated from parts ofdata lines in accordance with the direction in which an alignment filmis rubbed.

Another object is to provide a method of fabricating a liquid crystaldisplay which prevents the transmission of light generated from theparts of data lines in accordance with the direction of rubbing analignment film.

Additional features and advantages of the invention will be set forth inthe description which follows and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, in oneaspect the present invention includes: a thin film transistor platehaving a gate line, a data line, a gate electrode, a thin filmtransistor, a passivation layer, and a pixel electrode; a color filterplate including a black matrix, a color filter and a common electrode ona second transparent substrate; and liquid crystals injected and sealedbetween the thin film transistor plate and the color filter plate,wherein the black matrix of the color filter plate asymmetricallyoverlaps the data line of the thin film transistor plate.

The thin film transistor plate further includes: a gate line on a firsttransparent substrate; a data line arranged to cross the gate linewherein the gate line is insulated from the data line; a gate electrodeat the area where the gate line and data line cross, wherein the gateelectrode protrudes from the gate line; a thin film transistor having asource electrode connected to the data line and a drain separated fromthe source electrode, wherein the source and drain electrodes confronteach other; a passivation layer covering the thin film transistor,wherein a contact hole exposing a portion of the drain electrode isformed in the passivation layer; and a pixel electrode partiallyoverlapping the data line, wherein the pixel electrode is formed on thepassivation layer and is connected to the drain electrode through thecontact hole.

In another aspect, the present invention includes: a thin filmtransistor plate having a gate line, a data line, a gate electrode, athin film transistor, a passivation layer, and a pixel electrode; acolor filter plate including a black matrix, a color filter and a commonelectrode on a second transparent substrate; and liquid crystalsinjected and sealed between the thin film transistor plate and the colorfilter plate, wherein the pixel electrode asymmetrically overlaps twodata lines, one at each end respectively.

In a further aspect, the present invention includes: a thin filmtransistor plate having a gate line, a data line, a gate electrode, athin film transistor, a passivation layer, and a pixel electrode; acolor filter plate including a black matrix, a color filter and a commonelectrode on a second transparent substrate; and liquid crystalsinjected and sealed between the thin film transistor plate and the colorfilter plate, wherein a cut-off film which is asymmetrically overlappedby data line, and is partially overlapped by the pixel electrode, isformed under the data line.

In a further aspect, the present invention includes a method offabricating a liquid crystal display having a transparent substrate onwhich a gate line region and a data line region are defined, wherein themethod includes the steps of: forming a gate line in the gate region,wherein a gate electrode which protrudes from the gate line, and acut-off film which is overlapped asymmetrically by the data line region,are formed simultaneously; forming a data line in the data line regionon the transparent substrate, wherein the data line crosses and isinsulated from the gate line, and wherein a source electrode at one sideof the data line and a drain electrode which confronts and is isolatedfrom the source electrode are formed; forming a passivation layercovering the above structure, wherein a contact hole exposing a portionof the drain electrode is formed in the passivation layer; and forming apixel electrode connected to the drain electrode through the contacthole on the passivation layer, wherein the pixel electrode partiallyoverlaps the cut-off film.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 shows a layout of a unit pixel of a conventional TFT-LCD;

FIG. 2 is a cross-sectional view, which is bisected through the lineI–I′ in FIG. 1, of an LCD having a TFT with an inverse staggeredstructure according to a related art;

FIG. 3 shows a cross-sectional view bisected through the line II–II′ inFIG. 1;

FIGS. 4A to 4C show cross-sectional views, which are bisected throughthe line II–II′ in FIG. 1, of fabricating an LCD according to a relatedart;

FIG. 5A shows a graph of equipotential lines between a TFT array plateand a color filter plate in an LCD according to a related art, wherein apredetermined voltage is applied to the plates and illustrating thegeneration of a light-leakage region B when light is cut off by liquidcrystals between the plates;

FIG. 5B shows a cross-sectional view of an LCD where a light leakageregion is generated according to the related art;

FIG. 6 shows a layout of a unit pixel of a TFT-LCD according to a firstembodiment of the present invention;

FIG. 7 is a cross-sectional view bisected through the line III–III′ inFIG. 6;

FIG. 8 shows a cross-sectional view bisected through the line IV–IV′ inFIG. 6;

FIG. 9 shows a cross-sectional view of an LCD according to a firstembodiment of the present invention;

FIG. 10 shows a layout of a unit pixel of a TFT-LCD according to asecond embodiment of the present invention;

FIG. 11 is a cross-sectional view of an LCD having a TFT with an inversestaggered structure according to a second embodiment of the presentinvention, which is bisected through the line III–III′ in FIG. 10;

FIG. 12 shows a cross-sectional view bisected through the line IIII–III–IV′ in FIG. 10;

FIG. 13A shows a graph of equivalent potential lines between a TFT arrayplate and a color filter plate in an LCD according to a secondembodiment of the present invention art, wherein a predetermined voltageis applied to the plates;

FIG. 13B shows a cross-sectional view of an LCD according to a secondembodiment of the present invention;

FIG. 14 shows the width of a light leakage region corresponding to theoverlapped area between a data line and a pixel electrode adjacent tothe data line;

FIG. 15 shows a layout of a unit pixel of a TFT-LCD according to a thirdembodiment of the present invention;

FIG. 16 and FIG. 17 are cross-sectional views of an LCD bisected throughthe lines III–III′ and IV–IV′ in FIG. 15;

FIG. 18A to FIG. 18C show cross-sectional views of fabricating an LCDaccording a third embodiment of the present invention, which arebisected through the line IV–IV′ in FIG. 15;

FIG. 19A shows a graph of equivalent potential lines between a TFT arrayplate and a color filter plate in an LCD according to a third embodimentof the present invention art wherein a predetermined voltage is appliedto the plates;

FIG. 19B shows a cross-sectional view of an LCD according to a thirdembodiment of the present invention; and

FIG. 20A and FIG. 20B show the directions of rubbing alignment films ofa TFT array plate and a color filter plate in an LCD according to athird embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 6 to FIG. 9 illustrate a first embodiment.

FIG. 6 shows a layout of a unit pixel of a TFT-LCD according to a firstembodiment, FIG. 7 is a cross-sectional view bisected through the lineIII–III′ in FIG. 6, FIG. 8 shows a cross-sectional view bisected throughthe line IV–IV′ in FIG. 6, and FIG. 9 shows a cross-sectional view of anLCD according to a first embodiment.

Referring to FIG. 6 to FIG. 8, a gate line 100 is formed in a horizontaldirection on a transparent substrate 1′ as a TFT array plate on which aTFT and a pixel electrode are arranged. Data line 200 is formedperpendicular to the direction of gate line 100, which is insulated fromthe data line 200.

A gate electrode 140 protruding from the gate line 100 extends out inthe same direction as the data line 200 is arranged.

An active layer 120, above which a gate insulating layer 220 shown inFIGS. 7–8 lies, is formed under the gate electrode 140. A source region120 a and a drain region 120 c are defined at either side of a channelregion in the active layer 120.

A source electrode 160, which protrudes from the data line 200 and isconnected to the source region, and a drain electrode 180 connected tothe drain region confront each other separately, in the same directionin which the gate line 100 is arranged.

An organic passivation layer 240, as shown in FIG. 7 and FIG. 8, coversthe above structure. A contact hole exposing the drain electrode 180 isformed in the organic passivation layer 240. The organic passivationlayer 240 may be formed by coating the above structure with an organicinsulator such as acryl, BCB (benzocyclobutene) or the like.

A pixel electrode 300, which fills up the contact hole and is connectedto the drain electrode 180, is formed on the organic passivation layer240. The pixel electrode 300 overlaps a portion of the data line 200 bya width A′, which is usually under 1.5 μm to increase the opening ratio,wherein the organic passivation layer 240, which is an insulating layerhaving a low dielectric constant, lies beneath the pixel electrode 300.

A color filter consisting of R (red), G (green) and B (blue) patterns, ablack matrix 290 and a common electrode (not shown in the drawing) arefabricated in the color filter plate m′, as shown in FIG. 9, accordingto the first embodiment.

In an LCD according to the first embodiment, liquid crystals 280 areinjected to be sealed between the TFT array plate

and the color filter plate m′. The black matrix 290 of the color filterplate m′ has an asymmetrically-overlapped structure such that the blackmatrix 290 covers one portion of the data line 200 of the TFT arrayplate

An alignment film (not shown in the drawing) is formed over the colorfilter and TFT array plates m′ and

Namely, when the plates m′ and

are being sealed, the black matrix 290 of the color filter plate m′exposes most of the TFT array plate

except the TFT, the gate line 100 and the data line 200. In this case,the black matrix 290 is designed to partially overlap the data line 200.

The first embodiment, as shown in FIG. 6, thus has theasymmetrically-overlapped structure such that the data line 200 of theTFT array plate

is overlapped by the pixel electrode 300 by the width A′.

Then, liquid crystals 280 between the color filter and TFT array platesm′ and

in the LCD of the first embodiment are aligned uniformly by carrying outa rubbing process of rubbing the alignment film with cloth or the like.

Once a predetermined voltage is applied to the TFT array and colorfilter plates

and m′, the working directions of the liquid crystals 280 are changed.Namely, as shown in FIG. 9, the region at which the light transmissionis increased abruptly occurs from 1 μm to 2 μm near the pixel electrode300 as the working directions of the liquid crystals 280 are changed dueto the distortion of the liquid crystals 280 to predetermined degrees.The location of this light transmission region may be changed the fromthe right to the left of the data line in accordance with the directionof rubbing the alignment film.

As mentioned in the above description, this embodiment has the structurethat the data line 200 is asymmetrically overlapped by the pixelelectrode 300 and the black matrix 290. Thus, the region where the dataline 200 is overlapped by the black matrix 290 actually blocks theabove-mentioned region (which includes B′) where the light transmissionabruptly increases, to cut off light. Therefore, the light leakageregion B′ has no influence on the image quality.

FIG. 10 to FIG. 13B illustrates a second embodiment.

FIG. 10 shows a layout of a unit pixel of a TFT-LCD according to asecond embodiment.

FIG. 11 is a cross-sectional view of an LCD having a TFT with an inversestaggered structure according to a second embodiment, which is bisectedthrough the line III–III′ in FIG. 10.

FIG. 12 shows a cross-sectional view bisected through the line IV–IV′ inFIG. 10.

FIG. 13A shows a graph of equivalent potential lines between a TFT arrayplate and a color filter plate in an LCD according to a secondembodiment wherein a predetermined voltage is applied to the plates.

FIG. 13B shows a cross-sectional view of an LCD according to a secondembodiment.

FIG. 14 shows the width of a light leakage region corresponding to theoverlapped width between a data line and a pixel electrode adjacent tothe data line.

Referring to FIG. 10 to FIG. 13B, a gate line 100, as shown in FIG. 10to FIG. 12, is formed in a horizontal direction on a transparentsubstrate 1′ as a TFT array plate on which a TFT and a pixel electrodeare arranged. A gate electrode 140 protruding from the gate line 100extends out.

An active layer 120, underneath which a gate insulating layer 220 shownin FIGS. 11–12 lies, is formed over the gate electrode 140. A sourceregion, a channel region and a drain region are defined in the activelayer 120.

A data line 200, which is insulated from the gate line 100, is arrangedcross the gate line 100. The data line 200 has a source electrode 160and a drain electrode 180 which cover, respectively, the source anddrain regions of the active layer 120.

An organic passivation layer 240 covers the above structure. A contacthole exposing the drain electrode 180 is formed in the organicpassivation layer 240. The organic passivation layer 240 is formed withan organic insulator such as acryl, BCB (benzocyclobutene) or the like.

A pixel electrode 300 which fills up the contact hole and is connectedto the drain electrode 180 is formed on the organic passivation layer240. In this case, the pixel electrode 300, asymmetrically overlaps adata line 200 at both ends. As shown in FIG. 10, the width by which thepixel electrode 300′ overlaps the data line 200 at one end of the pixelelectrode is designated by the reference sign ‘a’. The width a rangesfrom 2 to 4 μm. The other width, by the pixel electrode 300 overlaps thedata line 200 at the other end of the pixel electrode, is designated bythe reference sign ‘b’ and is less than 2 μm.

As mentioned in the above description, a light leakage region is formedat the left or right of the data line 200 in accordance with thedirection of rubbing the alignment film. In order to block the lightleakage region, the LCD according to the second embodiment has theoverlapped structure wherein the data line 200 is overlapped by thepixel electrode 300 or 300′ to a width of at least 2 μm.

A color filter consisting of R (red), G (green) and B (blue) patternsand a black matrix 290 are fabricated on the color filter plate m′ inthe LCD according to the second embodiment.

In the LCD according to the second embodiment, liquid crystals 280 areinjected to be sealed between the TFT array plate

and the color filter plate m′. An alignment film (not shown in thedrawing) is formed in the color filter and TFT array plates m′ and

Liquid crystals 280 between the color filter and TFT array plates m′ and

are aligned uniformly by carrying out a process of rubbing the alignmentfilm with cloth or the like. The liquid crystals 280 change thecharacteristics of light transmission, provided that a predeterminedvoltage is applied to the plates.

The LCD having the structure such that a pixel electrode asymmetricallyoverlaps a data line at both ends, as shown in FIG. 13A and FIG. 13B,produces no light leakage, as explained in the following description byreferring to FIG. 13A and FIG. 13B.

FIG. 13A and FIG. 13B show a pattern of cutting off light due to theliquid crystal function when voltage is applied between the color filterand TFT array plates m′ and

which are in a normally white mode. Curves between both plates m′ and

are equipotential lines. Liquid crystals react with the equipotentiallines perpendicularly. FIG. 13A also shows the graph “P” indicating thepermeability of light in the device.

As shown in FIG. 13A and FIG. 13B, the curves are greatly distorted onthe data line 200 as the voltage of the data line 200 influences thevoltage applied to the liquid crystals 280. Thus, the region at whichthe light transmission is increased abruptly shows up 1 μm to 2 μm nearthe pixel electrode 300 as the working directions of the liquid crystals280 are changed due to the distortion of the liquid crystals topredetermined degrees. Yet, light actually fails to penetrate due to theoverlapped region between the data line 200 and its adjacent pixelelectrode 300′.

Particularly, there is a potential difference at the light leakageregion B′ due to the distortion of the crystals to predetermineddegrees. But, image quality actually is not affected as the light isblocked by the overlapped region between the data line 200 and theadjacent pixel electrode 300′.

The directions of the liquid crystals 280 are oriented by the rubbingdirections of each alignment film of the TFT plate

and color filter plate m′. The location of the light transmission regionmay be changed from right to left, or vice versa, of the data line 200in accordance with the direction of rubbing the alignment film.

In the LCD according to the second embodiment, as shown in FIG. 12, theoverlapped width “a” between the data line 200 and the pixel electrode300′ adjacent to the one side of the data line 200 ranges from 2 to 4μm. And, the other overlapped width “b” between the data line 200 andthe pixel electrode 300 adjacent to the other side of the data line isless than 2 μm.

FIG. 14 shows the width of a light leakage region corresponding to theoverlapped width between a data line and a pixel electrode adjacent tothe data line.

Referring to FIG. 14, the overlapped width between the data line and thepixel electrode adjacent to the data line should be at least 2 μm at theregion where the light leakage is generated. A maximum value of theopening ratio is attained because the width of the light leakage becomes0 to prevent the light leakage provided that the width is 2.5 μm. Whenthe overlapped width becomes greater than 4 μm, the opening ratio isreduced greatly. And, when the overlapped width becomes less than 2 μm,it is difficult to block the light leakage efficiently.

FIG. 15 shows a layout of a unit pixel of a TFT-LCD according to a thirdembodiment.

FIG. 16 and FIG. 17 are cross-sectional views of an LCD bisected throughthe lines III–III′ and IV–IV′ in FIG. 15.

FIG. 18A to FIG. 18C show cross-sectional views of fabricating an LCDaccording a third embodiment, which are bisected through the line IV–IV′in FIG. 15.

FIG. 19A shows a graph of equipotential lines between a TFT array plateand a color filter plate in an LCD according to a third embodimentwherein a predetermined voltage is applied to the plates.

FIG. 19B shows a cross-sectional view of an LCD according to a thirdembodiment.

FIG. 20A and FIG. 20B show the directions of rubbing aligrunent films ofa TFT array plate and a color filter plate in an LCD according to athird embodiment.

A third embodiment will be explained in the following description byreferring to FIG. 15 to FIG. 20B.

In an LCD according to a third embodiment, a gate line 100 is formed ina horizontal direction on a transparent substrate 1′ as a TFT arrayplate on which a TFT and a pixel electrode are arranged. Data line 200is formed perpendicular to the direction of the gate line 100.

A gate electrode 140 protruding from the gate line 100 extends out inthe same direction as the data line 200 is arranged.

An active layer 120, above which a gate insulating layer 220 lies, isformed beneath the gate electrode 140. A source region 120 a and a drainregion 120 b are defined at both sides of a channel region (which liesat the region corresponding to the gate electrode 140) in the activelayer 120.

A source electrode 160, which protrudes from the data line 200 and isconnected to the source region, and a drain electrode 180 connected tothe drain region are formed respectively, each arranged in a samedirection in which the gate line 100 is arranged.

A cut-off film 400, which is asymmetrically overlapped by the data line200 to the left or right direction of the data line 200, is patternedbelow the data line 200.

An organic passivation layer 240 covers the above structure. A contacthole exposing the drain electrode 180 is formed in the organicpassivation layer 240. A pixel electrode 300 connected to the drainelectrode 180 through the contact hole is formed on the organicpassivation layer. The pixel electrode 300 partially overlaps the dataline 200 and the cut-off film 400.

A color filter, a black matrix and a common electrode are fabricated inthe color filter plate m′ of an LCD according to the third embodiment.

In an LCD according to the third embodiment, liquid crystals 280 areinjected to be sealed between the TFT array plate

and the color filter plate m′.

A process of fabricating the LCD of the third embodiment will beexplained in the following description.

Referring to FIG. 16 and FIG. 15A, after a metal layer has been formedby sputtering Al, Mo or the like, on a transparent substrate 1′ such asglass, in which gate and data lines are defined, gate lines 100 areformed by patterning the metal layer.

In this case, a gate electrode 140 which protrudes from and the gateline 100 and a cut-off film 400, to be overlapped partially by the dataline region, are patterned as soon as the gate line 100 is patterned.The gate electrode 140 and the cut-off film 400 are etchedsimultaneously by using the same etch mask.

After a gate insulating layer 220 is formed to cover the gate electrode140, an amorphous silicon layer having been deposited successively, anactive layer 120 is formed by patterning the amorphous silicon layer.

Referring to FIG. 18B, after a metal layer is formed on the abovestructure, data lines 200 are patterned by etching the metal layer. Whenthe data lines 200 are patterned, source and drain electrodes 160 and180 connected to the source and drain regions respectively are alsopatterned. In this case, the source and drain electrodes 160 and 180 arearranged to cross the gate line 100. The data line 200 is patterned topartially overlap the cut-off film 400.

An organic passivation layer 240 is formed to cover the above structure.The organic passivation layer 240 is formed with an organic insulatorsuch as acryl, BCB (benzocyclobutene) or the like.

The organic passivation layer 240 which has excellent coverage enablesthe plate surface of an LCD to be planarized and reduces alignmentdegradation of liquid crystals due to the step difference. Thedielectric constant of the organic passivation layer 240 is lower thanthat of an inorganic insulating layer. Thus, when an LCD having a highopening ratio is fabricated by forming a pixel electrode 300 overlappingthe data lines 200 on the organic passivation layer 240, thedegradations such as flickering images are prevented, as no voltagedistortion due to parasitic capacitance at the overlap region betweenthe data line 200 and pixel electrode 300 occurs.

When BCB is used for the organic passivation layer, a thermal treatmentis carried out for an hour at 250° C. to 300° C. (the temperature isoptimal at 280° C.) and then the surface of BCB is treated with anoxygen ashing process. These processes improves the adhesion between theorganic passivation layer 240 and a transparent conductive layer to beformed, which prevents the erosion of the organic conductive layerduring subsequent processes.

Referring to FIG. 18C, a contact hole exposing the drain electrode 180is formed in the passivation layer 240.

After ITO (Indium Tin Oxide) has been deposited on the passivation layer240, a pixel electrode 300 is formed by patterning the ITO to beconnected to the drain electrode 180. The pixel electrode 300, asmentioned in the above explanation, has the structure overlapping thedata line 200. The width of the overlap area is at least 1.5 μm. Thedata line 200 and the cut-off film 400 are overlapped by a respectivepixel electrode 300 within a range between 2 μm and 4 μm.

When the overlap width between the pixel electrode 300, the data line200 and the cut-off film 400 exceeds 4 μm, the opening ratio is reducedgreatly. And, when the overlap width becomes less than 2 μm, it isdifficult to block the light leakage efficiently. Thus, the fabricationof the TFT array plate is completed

After liquid crystals 280 have been injected between the TFT array plate

and the color filter plate m′ in which color filters and a black matrixare fabricated, an LCD of the third embodiment, as shown in FIG. 19A andFIG. 19B, is completed by carrying out a sealing process. In this case,an alignment film shown in the drawing) is formed on the color filterplate m′ and the TFT array plate

Liquid crystals between the color filter and TFT array plates arealigned uniformly by carrying out a process of rubbing the alignmentfilm with cloth and the like.

As shown in FIG. 19A and FIG. 19B, the LCD having the structure suchthat the data line, the pixel electrode and the cut-off film areoverlapped has no light leakage in the third embodiment.

FIG. 19A and FIG. 19B show a pattern of cutting off light because of theliquid crystal function when voltage is applied between the color filterand TFT array plates m′ and

which are in a normally white mode. Curves between both plates m′ and

are equipotential lines. Liquid crystals react with the equipotentiallines perpendicularly. FIG. 19A also shows the graph “P” indicating thepermeability of light in the device.

As shown in FIG. 19A and FIG. 19B, the curves are greatly distorted onthe data line 200 as the voltage of the data line 200 influences thevoltage applied to the liquid crystals 280. Thus, working directions ofthe liquid crystals are changed and the region at which the lighttransmission is increased abruptly shows up 1 μm to 2 μm near the pixelelectrode. Yet, light actually fails to penetrate due to the cut-offfilm 400 under the data line 200 and the overlap region between the dataline 400 and its adjacent pixel electrode.

Particularly, there is a potential difference at the light leakageregion B′ due to the distortion of the crystals to predetermineddegrees. But, image quality actually is not affected as the light isblocked by the cut-of film 400.

In the LCD according to the third embodiment, it is preferred that theoverlap width between the data line, the pixel electrode and the cut-offfilm should be from 2 μm to 4 μm. When the overlap width becomes greaterthan 4 μm, the opening ratio is reduced greatly. When the overlap widthbecomes less than 2 μm, it is difficult to block the light leakageefficiently.

Moreover, the working directions of the liquid crystals 280 are changed,as shown in FIG. 20A and FIG. 20B, in accordance with the rubbeddirection of each alignment film on the color filter plate and the TFTarray plate, which may change the location of the light leakage regionto the left or right of the data line 200. Therefore, the location ofthe cut-off film may depend on the location of the light leakage region.

As mentioned in the above description, the first embodiment has thestructure that the data line is overlapped asymmetrically by the pixelelectrode and the black matrix. Thus, the region where the data line isoverlapped by the black matrix actually blocks the light leakage.Therefore, the light leakage region around the data line is blocked bythe overlap region in accordance with the direction of the alignmentfilm.

In the second embodiment having the structure that the data line andboth stages of the pixel electrode adjacent to the data line overlapasymmetrically, light is unable to be transmitted as the light leakageregion at each side of the data line is cut off by the overlap regionbetween the data line and the pixel electrode in accordance with thedirection of rubbing the alignment film.

In the third embodiment, the light leakage caused by the rubbingdirection is prevented by the cut-off film, as the cut-off film isoverlapped by the data line and the pixel electrode asymmetrically.

Therefore, image quality and reliability of the product are improved asthe light leakage is effectively prevented by the first to thirdembodiments.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in a liquid crystal display anda fabricating method thereof of the present invention without departingfrom the spirit or scope of the inventions. Thus, it is intended thatthe present invention cover the modifications and variations of thisinvention provided they come within the scope of the appended claims andequivalents.

1. A liquid crystal display having a plurality of pixels, each pixelcomprising: a gate line on a first transparent substrate; a data linearranged to cross the gate line wherein the gate line is insulated fromthe data line; a gate electrode protruding from said gate line near anarea where said data line crosses said gate line; a thin film transistorhaving a source electrode connected to the data line and a drainelectrode separated from the source electrode; a passivation layercovering the thin film transistor wherein a contact hole exposing aportion of the drain electrode is formed in the passivation layer; apixel electrode on the passivation layer, the pixel electrode beingconnected to the drain electrode through the contact hole and partiallyoverlapping the data line; a black matrix, a color filter and a commonelectrode on a second transparent substrate, the black matrix beingextended along the data line to overlap partially and asymmetricallywith the data line; and liquid crystals provided and sealed between thefirst and second transparent substrates.
 2. The liquid crystal displayaccording to the claim 1, wherein a location where the black matrixoverlaps the data line is selected according to a direction of rubbingan alignment film.
 3. The liquid crystal display according to the claim1, wherein the passivation layer is an organic passivation layer.
 4. Theliquid crystal display according to the claim 3, wherein the organicpassivation layer is made of acryl.
 5. The liquid crystal displayaccording to the claim 3, wherein the organic passivation layer is madeof BCB.
 6. The liquid crystal display according to the claim 1, whereina portion of the black matrix that partially overlaps the data line hasa width of about at least 2 μm.
 7. A liquid crystal display comprising:a thin film transistor plate further comprising: a gate line on a firsttransparent substrate, a data line arranged to cross the gate linewherein the gate line is insulated from the data line, a gate electrodeprotruding from said gate line near an area where said data line crossessaid gate line, a thin film transistor having a source electrodeconnected to the data line and a drain electrode separated from thesource electrode wherein the source and drain electrodes confront eachother; a passivation layer covering the thin film transistor wherein acontact hole exposing a portion of the drain electrode is formed in thepassivation layer; and a pixel electrode on the passivation layer andbeing connected to the drain electrode through the contact hole, whereinthe pixel electrode partially overlaps the data line; a color filterplate including a black matrix, a color filter and a common electrode ona second transparent substrate; and liquid crystals provided and sealedbetween the thin film transistor plate and the color filter plate,wherein a cut-off film is formed under the data line, an edge portion ofthe cut-off film is overlapped by an edge portion of the data line, andan overlap length between the edge portion of the cut-off film and theedge portion of the data line is substantially the same as an overlaplength between the pixel electrode and the data line.
 8. The liquidcrystal display according to claim 7, wherein the passivation layer isan organic passivation layer.
 9. The liquid crystal display according toclaim 7, wherein the cut-off film and the gate line are formed on a samelevel.
 10. The liquid crystal display according to claim 7, wherein anoverlap region between the pixel electrode, the cut-off layer and thedata line has a width between 2 μm and 4 μm.
 11. The liquid crystaldisplay according to claim 7, wherein the cut-off film is formed at oneside of the data line, said side selected according to a direction ofrubbing an alignment film.
 12. A method of fabricating a liquid crystaldisplay having a transparent substrate on which a gate line region and adata line region are defined, comprising: simultaneously forming a gateline in the gate region wherein a gate electrode protrudes from the gateline, and a cut-off film; forming a data line in the data line region onthe transparent substrate, wherein the data line crosses and isinsulated from the gate line, and wherein a source electrode is formedat one side of the data line, and wherein a drain electrode is formedwhich confronts and is isolated from the source electrode; forming apassivation layer covering the gate line region, the data line regionand the cut-off film, wherein a contact hole exposing a portion of thedrain electrode is formed in the passivation layer; and forming a pixelelectrode connected to the drain electrode through the contact hole onthe passivation layer, the pixel electrode partially overlapping thedata line, wherein an edge portion of the cut-off film is overlapped byan edge portion of the data line, and an overlap length between the edgeportion of the cut-off film and the edge portion of the data line issubstantially the same as an overlap length between the pixel electrodeand the data line.
 13. The method according to claim 12, wherein thepassivation layer is an organic passivation layer.
 14. The methodaccording to claim 12, wherein the cut-off film and the gate line areformed on a same level.
 15. The method according to claim 12, an overlapregion between the pixel electrode, the cut-off layer and the data linerange has a width of between 2 μm and 4 μm.
 16. A liquid crystal displaycomprising: a first transparent substrate; a gate line on the firsttransparent substrate; a data line arranged to cross the gate linewherein the gate line is insulated from the date line; a thin filmtransistor having a source electrode connected to the data line, a drainelectrode separated from the source electrode, and a gate electrodeconnected to said gate line in an area where said data line crosses saidgate line; a passivation layer over the thin film transistor and havinga contact hole exposing a portion of the drain electrode; and a pixelelectrode formed on the passivation layer and being connected to thedrain electrode through the contact hole, the pixel electrode partiallyoverlapping the data line; a cut-off film under the data line, whereinan edge portion of the cut-off film is overlapped by an edge portion ofthe data line, and an overlap length between the edge portion of thecut-off film and the edge portion of the data line is substantially thesame as an overlap length between the pixel electrode and the data line;a second transparent substrate including a black matrix, a color filterand a common electrode; and liquid crystals between the first and secondtransparent substrates.